Bleomycin is a clinically useful antitumor antibiotic employed for the treatment of squamous cell carcinomas and malignant lymphomas. Bleomycin can form several redox-active metal complexes that are capable of DNA strand scission and it is this oxidative transformation that is believed to be responsible for its utility as an antitumor agent. The objectives of this study are a better understanding of the way in which bleomycin is activated, the chemical nature of the activated intermediate(s) and the mechanism by which activated bleomycin mediates DNA degradation.